Billie Jean King has described Roger Federer as a "champion's champion" after the Swiss maestro announced his retirement from tennis.

Having not played competitively since Wimbledon 2021, Federer revealed on Thursday he had taken the "bittersweet decision" to retire.

After being beset by injuries in recent years, Federer declared: "I've worked hard to return to full competitive form. But I also know my body's capacities and limits, and its message to me lately has been clear."

Federer will make a farewell appearance at the Laver Cup in London next week, partnering with fellow greats Rafael Nadal and Novak Djokovic for Team Europe.

The 41-year-old will end his career with 20 grand slam singles titles, a tally only bettered by Nadal (22) and Djokovic (21) in the men's game, but King believes he was the most complete player of the modern era.

"Roger Federer is a champion's champion," King, herself the winner of eight Open-era major singles titles, wrote on Twitter.

"He has the most complete game of his generation and captured the hearts of sports fans around the world with an amazing quickness on the court and a powerful tennis mind. 

"He has had a historic career with memories that will live on and on.

"Congratulations @rogerfederer, we wish you the very best as your journey continues."